There are numerous suggestions in the prior art which are used to transfer a rotational motion of an electric motor into a linear motion of an attached actuation device. Some of the prior art documents are listed below:
The document JP-A-58-192451 discloses a linear actuator having a reduced inertial moment. A stepping motor is mounted on a base, with which shaft supporting pieces are provided integrally on both sides. The motor has ring shaped stators, and a ring shaped rotor magnet. A cam unit is formed at a rotary disk which supports the magnet. When the coils provided on the stators are energized, the magnet and the disk are rotated, with the result that the cam unit formed on the disk is rotated. Thus, a pin moves along the groove of the cam unit, a head frame which is engaged with the cam unit through the pin moves on a shaft and slides on a magnetic disc.
As disclosed in Allen et al., U.S. Pat. No. 4,496,865, issued Jan. 29, 1985, entitled "Methods and Apparatus For Translating Electric Motor Rotation Into Linear Travel", the rotational motion of the electric motor is translated into a linear motion by a linearly traveling device. This linearly traveling device is restrained against rotation at points peripherally distributed relative to the device. In particular there is a pair of interfitting parts including a linear keyplate and a keyway at each of the peripheral distributed points. One of these interfitting parts is connected to the linearly travelling device and the other of these parts is maintained stationary relative to that one interfitting part.
As disclosed in Conrad, U.S. Pat. No. 4,607,197, issued Aug. 19, 1986, entitled "Linear and Rotary Actuator", a cylindrical movable member or armature is provided which is mounted for both axial movement and for angular movement about its axis. The armature member has teeth on its surface formed in both axial rows and in circumferential alignment or rows. Stator means having poles with windings associated with the poles is provided, the stator means having a central opening in which the movable armature member is mounted for angular and axial movement. By energizing certain angularly spaced windings, the movable armature member may be caused to rotate. By energizing certain axially spaced windings, the movable member of the armature can be caused to move axially. Simultaneous angular and axial movement is achieved by energizing appropriate windings.
As disclosed in Dietrich et al., U.S. Pat. No. 5,731,640, issued Mar. 24, 1998, entitled "Converter for Changing Rotary Movement to Axial Movement", the device has a spindle, a spindle nut surrounding the spindle, and a plurality of rollers. Each of the rollers has a groove profile corresponding to a thread in the spindle and roller grooves corresponding to spindle grooves formed on the interior of the spindle nut. The converter device is driven by a drive unit such as an electric motor, either via the elements spindle nut and spindle or, with an interposed connection element, via the rolling elements or rollers. The converter device has a reset device with a mechanical energy accumulator and an energy delimiter. Energy transfer takes place from the electric motor via the energy delimiter to energy accumulator connected to a casing or vice versa.
Another approach for providing a mechanism which imparts a motion to a moving body is disclosed in the patents by Zumeris: U.S. Pat. No. 5,453,653, issued Sep. 26, 1995, entitled "Ceramic Motor," and U.S. Pat. No. 5,616,980, issued Apr. 1, 1997, entitled "Ceramic Motor". Both patents disclose a ceramic micromotor for moving a body. The ceramic motor comprises a piezoelectric plate to which electrodes are attached. Additionally a ceramic spacer is mounted to the piezoelectric plate and in operation, the spacer is pressed against the moving body. Spring loading is provided to reduce the effects of wear and to provide a degree of shock protection for the piezoelectric ceramic. In a preferred embodiment spring loaded supports are applied in order to provide pressure between the ceramic spacer and the moving body which causes the motion of the ceramic spacer to be transmitted to the moving body. A conversion circuitry is necessary to drive the ceramic motor.
The drawback of the devices as disclosed in U.S. Pat. No. 5,453,653 and U.S. Pat. No. 5,616,980, is that the ceramic structure which provides the mechanical motion, needs to be driven by an electric circuit which applies voltages in the range between 30 and 500 volts AC. Therefore the use of the ceramic motors in battery powered devices require an additional conversion circuitry for providing the required voltage.